The present invention relates to recuperative heat exchangers and, more particularly, to tubular heat exchangers of the type wherein a heating fluid is passed over a plurality of heat exchange tubes arranged in laterally adjacent modules interconnected to provide a serpentine flow path through which a fluid to be heated is passed in heat exchange relationship with the heating fluid.
In a typical recuperator heat exchanger of the type to which the invention pertains, a number of heat exchange modules are disposed in a spaced array, laterally adjacent to each other. Each heat exchange module comprises a plurality of longitudinally disposed tubes mounted at their opposite ends to apertured tube sheets. The laterally adjacent ends of neighboring modules are interconnected in fluid communication to form a serpentine flow path through which the fluid to be heated passes from module to module through the heat exchange tubes in heat exchange relationship with the heating fluid which is being passed in cross flow over the outside of the heat exchange tubes of the array of heat exchange modules.
As the heat exchange modules are disposed in series with respect to the flow of the heating fluid thereover, the temperature of the tubes of the module disposed at the hot end of the heat exchanger, i.e., at the end where the heating fluid enters the heat exchanger, will be higher than the temperature of the tubes of the module disposed at the cold end of the heat exchanger, i.e., at the end where the heating fluid leaves the heat exchanger. Accordingly, the axial elongation upon heating and the axial contraction upon cooling of the heat exchange tubes differs over the extent of the heat exchanger with the amount of thermal deformation decreasing in the direction of the flow of the heating gas flowing therethrough. Due to the presence of this differential thermal deformation along the axis of the heat exchange tubes, provision must be made for the exchange modules to expand longitudinally without interference from support apparatus or the heat exchanger housing.
One known method to accommodate the thermal deformation of a heat exchange module is to fixedly support one end of the module while slidably supporting the opposite end thereof and providing a flexible bellows seal between the end of the module which is free to move axially and the inlet duct to the module, such as disclosed in U.S. Pat. No. 2,653,779. The thermal deformation of each module is taken up by the bellows seal associated therewith. Such bellows seals, however, are subject to cycle fatigue causing cracking and tearing after repeated heating and cooling of the heat exchange modules.
Another known solution is disclosed in U.S. Pat. No. 2,965,358 wherein resilient moveable seals are provided between adjacent modules and also between each module and the entrance and exit ducts thereto. Thermal deformation is accommondated by moveable seals provided between sections of the heat exchanger which move relative to each other. The seals are arranged in guides to direct their movement. Such a seal system is necessarily quite complicated.
Accordingly, it is an object of the present invention to accommodate thermal deformation of laterally adjacent heat exchange modules without resorting to expansion joints or flexible seals as a means of accommodating such thermal deformation.